Rooftop solar and battery storage are increasingly popular residential energy assets that provide homeowners with clean electricity when they need it most. In an era when electricity prices are steadily rising, and the country’s aging grid is increasingly vulnerable to natural disasters, solar and storage can save you money by offsetting utility consumption during peak periods, earn you credits for sending any excess power into the grid, and keep the lights on during a blackout.
Does the EV have a place among these distributed energy resources? Of course! EVs could integrate harmoniously with the grid as another form of storage, and power the home when warranted.
Here is a breakdown of the different ways EVs are starting to be integrated into existing residential DC power ecosystems and the grid at large.
Grid-tied
1. V1G
What’s required: a Level 2 AC charger, an EV, signing up for a time-of-use program
This basic form of load shifting may be familiar to current utility customers. The concept is simple: homeowners are incentivized to consume less electricity during certain high-demand periods in order to help balance the grid.
If not using a smart EV charger, the customer may need to physically unplug their vehicle, or manually schedule a charging session that complies with the utility program’s terms.
V1G and its ilk (demand response, emergency load reduction, etc.) are part of what dcbel’s Chief Growth Officer Matthieu Vidricaire calls the first generation of energy programs. “Those were great first steps considering the limitations of available residential solutions – the idea being ‘Please don’t charge your EV at 6:00 PM because you’re not helping,’ right?”
These programs and the terms used to describe them still hold relevance today, but are quickly evolving to fully embrace the benefits of bidirectional power flow.
“What does that tell us? This is fluid.”
2. V2G
What’s required: a bidirectional EV, bidirectional charger, interconnection agreement
The regulatory framework that supports vehicle-to-grid (V2G) is already mostly in place from solar and home battery grid injection programs – which themselves are products of the so-called first-generation of load management.
Take solar curtailment, for instance. This ability to disable injection of solar production because there’s too much of it already on the grid naturally invites the opposite approach: to inject on command, at times when the grid needs it the most. Vidricaire notes that home batteries like the Tesla Powerwall led the charge on this.
With V2G, EVs turn into batteries on wheels. Cheaper on a per-kWh basis and more ubiquitous than home batteries, EVs have great potential to give the grid a lift. The California Energy Commission projects upwards of 8 million EVs in the state by 2030 with a combined power of at least 60 gigawatts. That exceeds the highest electricity demand ever recorded in California by 8 gigawatts. As Ellie Cohen, CEO of The Climate Center pointed out during the state Senate introduction of a bill that would mandate that all EVs be bidirectional starting in 2027, “If we use even a tiny percentage of that EV capacity, we can secure a more reliable power grid.”
V2G pilot projects are proliferating in Europe, Australia and elsewhere. In the US, trials involving school buses and other commercial fleets are becoming more common. California’s Emergency Load Reduction Program is one of those first-gen programs that has since expanded its scope to include V2G payouts.
Like V1G, participation in V2G programs is entirely voluntary. As the smart grid evolves, so will V2G: picture real-time grid signals and a dynamic residential energy market.
Home integration
3. V2H self-consumption
What’s required: Bidirectional EV, bidirectional charger
We appreciate the way Jacqueline Piero, US Head of Policy & Regulatory at the Mobility House, rejects the notion that bidirectional charging will evolve in a linear way. It’s easy to assume that the development of vehicle-to-home (V2H) is a precursor to V2G becoming widespread. Instead, Piero puts both tracks on their own separate development paths, acknowledging that they exist in two different spheres and are being developed concurrently.
The V2H side of the bidirectional coin is naturally all about the home, allowing a vehicle to supply a house with power while respecting building safety codes and avoiding unintentional grid injection.
If you want to offset your home’s consumption at strategic times using energy stored in your vehicle, you can do so with an appropriately-wired bidirectional EV charger containing an inverter that acts as a current source and is grid following, which according to the IEEE means that it tracks the voltage angle of the grid to control its output.
The relatively simple nature of this setup can get homeowners on the fast track to savings, says Vidricaire. That’s because it doesn’t involve obtaining an interconnection permit, a process that can take several weeks.
“Imagine that I have an EV parked in my driveway at 6:00 p.m. and a smart device that knows energy is expensive at that time based on time-of-use rates. It can automatically orchestrate V2H self-consumption for an hour or two on my behalf and power my home with EV energy; I don’t have to push any buttons.
Later, it tops up my EV battery during off-peak hours. That’s a no brainer, right?”
This strategy, also called energy arbitrage, really does pay off. In California, evening peak rates can be up to 75% higher than off-peak rates. Leveraging EV energy for just an hour per day could save a family household hundreds of dollars per year in energy costs just by using an energy asset they already own.
“It’s amazing how just a small percentage of EV energy could lead to such a noticeable bottom-line benefit for homeowners.”
4. Blackout power
What’s required: Automatic Transfer Switch (ATS), Uninterruptable Power Supply (UPS), bidirectional charger, bidirectional EV
Blackout protection is a highly sought-after V2H application in the US, particularly in territories where grid stability is affected by severe weather. This system offsets a different kind of cost – namely, the risks and consequences associated with power outages. They can pose an inconvenience to some and grave danger to others, but everyone can agree that avoiding their effects is essential to maintaining consistent quality of life.
V2H provides emissions-free power for several days at a time during outages (depending on the capacity of your EV battery and your consumption habits).
To make this possible, the inverter inside the bidirectional charger will act as a voltage source instead of a current source and is grid forming – replacing the grid AC wave instead of following it like in the previous scenario.
Regarding the other requirements: The ATS is a peripheral device that will detect the power failure and switch your home over to EV power.
Meanwhile, the purpose of the UPS is to keep power flowing to the bidirectional charger just long enough so it can function properly during that critical moment when grid power is lost.
Understanding these differences is key
Bidirectional EVs and EVSE are making their way to your driveway. Once you take stock of all the ways bidirectional charging can make your life easier (and your energy bill smaller), you’ll be ready to choose the solution that works best for you.
With next-generation Home Energy Stations, consumers will become accustomed to having all the features described above seamlessly combined and auto-managed by one device that is both grid following and grid forming.
